Oh, something like it might exist, out there in the hidden corners of videogame-land. I've just never seen it.

Let's cut to the chase. My recommendation:

Go play it. We can talk spoilers next week.

But okay, okay. If you really want a full review, read on. Spoilers for The Last of Us and some minor spoilers for Left Behind follow.

Left Behind is a downloadable expansion for the widely loved (and Kotaku Game of the Year-winning) PS3 game The Last of Us. It's out today. If you, like so many others, got caught up in the story of Joel and Ellie, of the infection and the survivors and the moved-on world, then it's been made just for you.

How do you make a downloadable add-on for a game like The Last of Us? How do you continue a story that ended so well? Maybe you go back to the beginning. It's a fitting approach, seeing as how The Last of Us ended with the beginning—there at the story's end, Ellie finally revealed to Joel how she was bitten and what kept her going over the course of their journey:

"Back in Boston, back when I was bitten… I wasn't alone. My best friend was there, and she got bit too. We didn't know what to do. So she says, 'Let's just wait it out, y'know, we can be all poetic and just lose our minds together.'

I'm still waiting for my turn. Her name was Riley, and she was the first to die."

Left Behind tells the story of Riley and Ellie on that fateful day in Boston. It picks up a chunk of time after the end of American Dreams, the terrific prequel comic co-authored by The Last of Us writer Neil Druckmann and comics artist Faith Erin Hicks. (While the new story stands on its own, I strongly suggest reading American Dreams before playing Left Behind.)

Earlier this week I asked Druckmann what the title "Left Behind" actually refers to. He said there was no definitive answer, but laid out a few possibilities: The idea of Ellie leaving Riley behind, or possibly Ellie's fear of leaving Joel behind. However, the one he says he believes the most is the idea of leaving your childhood behind. "The idea that there's no going back after this," he said. "This is a turn for Ellie; after this event [she becomes] the Ellie you know from the main journey."

Left Behind takes place at a shopping mall—well, two shopping malls, actually. It's framed as a split-timeline story, with the present-day story picking up immediately after Joel is impaled at the university in the main game. Joel has been direly wounded and Ellie must leave him, unconscious and slowly dying, to scavenge medical supplies from a snow-covered shopping center nearby.

While Ellie sneaks and scrounges, the narrative periodically flashes back to an earlier, more peaceful time in her life. It's summer in Boston, before she met Joel and Tess. Riley has abruptly returned after leaving Ellie alone for months with no warning or explanation. After some prodding from Riley, the two sneak out of Ellie's military school and explore a deserted mall, all the while cautiously attempting to repair their dented friendship.

As they make their way through the abandoned mall, the two girls goof around, stopping off in stores to peruse the merchandise, trading riddles and jokes, and reminiscing on times past. Their playful teenage hijinks include some of the story's most lovely surprises. It's so rare for a video game to allow us to simply play in the way that Riley and Ellie do in Left Behind. (That something that comes so naturally in the real world could be so seemingly difficult to re-create in a medium dedicated to playfulness!) The fact that Left Behind accomplishes the feat so regularly is remarkable. There is so much joy here.

The split-narrative framing is a clever way to allow Ellie—who, after all, only learned the art of combat under Joel—to kick ass from time to time while still focusing the story on her comparatively peaceful life in Boston. Combat is sparse even in the present-day parts of Left Behind, but the mix feels good. Notably, several encounters have Ellie squaring off against hunters and infected at the same time, playing the two off of one another. The concept isn't as fleshed-out as it might have been, but it's still a refreshing evolution of the combat in the main game.

The flashbacks and flash-forwards bounce off of one another with a consistently well-tuned rhythm, and the contrast between the two serves an important narrative function. Ellie's relationship with Riley takes on a new layer when viewed as a parallel to her very different relationship with Joel. Each time the sticky Boston summer cuts to the hopeless Colorado winter, the similarities—and differences—between Ellie's two sets of circumstances receive an emphatic underline.

Ashley Johnson remains excellent in her role as Ellie. Thanks largely to her performance (and to the animation and mo-cap wizards at Naughty Dog), I've become utterly convinced by the character. Ellie easily carries Left Behind, as I'm sure she could easily carry a much longer game. As she self-consciously talks to herself and warily questions her friends, I don't hear an actor playing a role, I hear… well, I hear Ellie. Riley's actor Yaani King proves a fine match for Johnson, and their duet over the course of Left Behind illuminates the quiet corners of a friendship with great nuance and humor.

The entirety of Left Behind has been crafted with an exceptional degree of care and attention to detail, and it's extremely well-paced. Comparatively brief though it may be, the DLC manages to fit more peaks, valleys, and meaningful moments into its brief runtime than most mainstream games can manage in a dozen or more hours. In some ways even more so than The Last of Us itself, Left Behind feels like the work of creators unafraid to challenge themselves and stretch out, to see what new joys and sorrows they can conjure.

There is much more to say about Left Behind. Of course there is. For now: The Last of Us: Left Behind is beautiful. Play it. Take your time. We won't see anything like it for a good long while.